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User blog:Samuli.seppanen/Attaching the rungs
The new little ladder made from 6mm (unhardened) spring steel is shaping up nicely. Today I finished sawing and filing the slots into the ends of the tenons: The field frames snapped into the slots beautifully, and when there, the little ladder beams bend outwards only very slightly. I now consider the "little ladder beams should be 3 dactyls from each other"-mystery solved in an elegant fashion. I had played with the idea of using a fancy wedge system to bind the crosspiece and the little ladder beams together. The idea was to allow easy dismantling the entire little ladder, which could prove useful if/when I create a second set of field frames for the sinew torsion springs. In the end I came to my senses and just riveted the thing together: If I need to detach the crosspiece, I can just file away one end of the rivet and be done with it in 10 minutes. Another 20 minutes and I have riveted the thing back together. After riveting the crosspiece I decided to try to improve and strengthen the attachment of the little ladder to the rungs. I had initially used heavy wood screws, just like I had used with my previous little ladder. While they had worked quite well, they would get loose over time. So I tried using a few things: * Replacing the screws with bolts that have non-cutting threads. The shallow threads became loose after a few tightenings and loosenings and could not be trusted. * Bolt with its heads sunk below the surface of the rung at one end, and the threaded end projecting from the other end. The idea was to push the threaded end through the hole in the little ladder beam and use a bolt to tighten the package. Each rung would have had two of these bolts facing in opposite directions. This seemed like a good idea, except that it was impossible to bend the beams outwards enough to get the holes and the ends of the bolts match. So both attempts at improving the situation failed. However, the cheiroballistra manuscript mentions this: "And let the rungs and the crosspiece be lowered to the holes of the beams, and let the ends of the tenons of the cross-piece grasp next to the beams, so that they hold the beams together and that there is an aperture of 3 dactyls between them." Note that no mention is made of the tenons of the rungs grasping the little ladder. One would think riveting or something is required to keep the little ladder in one piece, but that might not actually be the case: * The rivet of the cross-piece binds the little ladder together. That part of the little ladder is extremely strong. * The field frame bars fit snugly into the slots in the little ladder beam tenons, and the package is tightened with wooden wedges. There is no way the little ladder beams can move outwards a this point, either. This means that there is no need to overdo the attachment of the little ladder beams and the rungs. Basically simple round steel bars pushed into matching holes in the rungs should do the trick, because of how pullback forces are distributed to the little ladder. Incidentally this would fit nicely with my interpretation of the little ladder beam tenons: the beams have to be bent outwards quite a bit when inserting the field frame bars into the slots in the tenons. Tightly riveted rungs would prevent inserting the field frames into the field frames. A round steel rod, however, would allow the beams to bend outwards without difficulty, without jeopardizing the integrity of the entire construction. I also reasoned that if a tight package is necessary, a simple rivet going in a slight angle from one beam to the other through the rung would make most sense. It would be be the strongest and simplest solution. Category:Blog posts Category:Backup Category:Little ladder Category:Practical